While chatting this morning with my cousin he asked if I knew why there seems to be so little similarity between Classical Roman Names and surnames found in Italy today. He is currently reading "The First Man In Rome" by Colleen McCullough which, as you may know, is almost overbearing in its use of the classical form of historical Roman names. I didn't really have a good answer so decided to do a little research on the web. According to Wikipedia, Italian names are mostly derived from Latin, but since Italy has been often ruled by foreigners, many surnames are of Spanish, French, German, Norman or Swiss origin. Another view can be found at the Mayrand Family Association – Meaning and Origin of Names:

In early times, the Romans had only one name. However, they later changed to using three names. The given name stood first and was called a "praenomen." This was followed by the "nomen" which designates the gens, or clan. The last name designates the family and is known as the "cognomen," Some Romans added a fourth name, the "agnomen," to commemorate an illustrious action, or remarkable event.

As the Roman Empire began to decline, family names became confused and single names once again became customary.During the early Middle Ages, people were referred to by a single given name. But gradually the custom of adding another name as a way to distinguish individuals gained popularity. Certain distinct traits became commonly used as a part of this practice. For instance, the place of birth: St. Francis of Assisi; a descriptive characteristic: Lambert Le Tort, an Old French poet whose name means "Lambert the Nisted;" the person's occupation: Piers, Plowman; or the use of the father's name: Leif Ericsson.